The three popular focusing mechanisms available on the astronomy market--rack and opinion, helical, and Crayford focusers, are specifically designed for rough, course focusing movements used in eyepiece viewing of the celestial heavens. Astro photography, also known as astro imaging, requires a focusing mechanism which is capable of a finer, more measured incremental change of focal length. The availability of digital cameras and computers has stimulated interest in astro imaging and augmented the demand for a focuser which is capable of accurate and fine incremental movements without any lateral shift.